Is NULL guaranteed to be 0?

Question

I was wondering if NULL is guaranteed to be 0 in C++, so I searched and came across these:

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This answer states that:

Answer 1

I think its fine practice to assume so. Having said that, it would be horrible practice to #undef NULL and or redefine it as something else. So long story short, it's not a 100% guarentee because it is possible to be something else, but it NEVER should be.